Compute For the Subtotal for Transaction Saved Searches

1. Navigate to Reports > Saved Searches > All Saved Searches > New.
2. Choose Transaction.
3. Under Criteria tab > Standard subtab, set Main Line = T.
4. Click the Results tab > Columns subtab, set the following:
    - Date
    - Name
    - Document Number
    - Formula (Currency) 
        Formula = {amount} - nvl({taxtotal},0) - nvl({shippingamount},0)
        Label = Subtotal
    - Amount (Tax Total)
    - Amount (Shipping)
    - Amount
5. Click Save & Run.
 
Note: The Subtotal is net of discount if added as line item.

Alternative for Formula (Currency):

    - Formula (Numeric) = nvl({totalamount},0)-nvl({discountamount},0)-nvl({taxtotal},0)-nvl({shippingamount},0)
        Label = Subtotal